In nature, many creatures are able to move through the air easily, gracefully and swiftly. Man has always dreamed of equaling this natural motion through the atmosphere, but to date has been essentially unable to do so. Birds, insects and even mammals are able to fly with flapping wings. Through eons of natural selection, fliers have developed advantages that make them highly capable and efficient at moving in air. Although the use of rotating propellers and jet action has allowed man to effectively move through air and therefore accomplish amazing things, a full understanding of the principles behind efficient flapping motion still eludes scientists.
A flapping flying device is presented herein, an ornithopter, which utilizes some of the principles perfected by nature through millions of years of evolutionary trial and error. Of course, all aspects of natural flapping are not addressed, since natural phenomena are complex and hold many secrets yet to be unveiled.
Some studies, as shown in the referenced prior art U.S. Pat. No. 5,401,196 indicate that propulsion by natural flapping motion, at least through water, is somewhat dependent upon vortices created by the flapping. Additionally, flapping propulsion is significantly more efficient than human methods of propulsion through fluids. The similarities between flapping in water for propulsion and flapping in air for propulsion suggest that the same principles are in effect. A vortex is created during a sweep in the fluid by a flexible foil which thereafter affects and provides impetus for a subsequent sweep of the wing or fin in the opposing direction. The instant invention utilizes this concept for propulsion of the device through air.
Human attempts to mimic the flapping motion of creatures have been for the most part unsuccessful. Flying devices as shown in the prior art U.S. Pat. No. 5,899,408 are such attempts. Most of these designs are not viable. Smaller ornithopters do fly, but at present do not compare in practicality to conventional propeller-driven aircraft.
The instant device for employing flapping motion for propulsion through air is both novel and unanticipated. It explains the heretofore mysterious success of movement by many flying and swimming creatures, A fundamental principle presented herein is that natural flapping utilizes a springboard-like highly elastic method to facilitate flapping and greatly conserve energy. Natural flapping of a wing or a fin is the action of a damped spring pendulum having a proximal end firmly communicated with the body of the organism and a distal end which elastically reacts with the fluid. This spring pendulum, or springboard, acts in a manner similar to a common diving board, wherein the distortion of the springboard in one direction stores potential energy which is released in a subsequent reverse movement. Once the wings are oscillating, the creature must add enough energy to overcome the damping caused by reaction with the fluid and energy losses due to internal friction. In an ideal situation, with no friction and in a vacuum, a single stroke would create an oscillation which would continue forever. Of course, friction does certainly exist, and reaction with air is necessary to keep an organism aloft, so a creature in nature is required to use muscle power to fly.
Observation of birds suggests that these organisms flap at a frequency unique to the creature. They seem to vary from this frequency only when acceleration is necessary, such as when starting, stopping and maneuvering. Additionally, organisms having larger wingspans flap at a lower frequency than smaller organisms, a characteristic which is further suggestive of a springboard pendulum since physics dictates that the period of vibration increases with the length of the pendulum. The springboard effect is somewhat disguised when observing these fliers, since soaring and accelerating conditions are common during the daily routine of the creatures. It is an effect which is, however, detectable during sustained flapping over long distances. It is also notable that minimal or no musculature is necessary at the wing extremities in the proposed flapping propulsion presented herein. The action of the wing is largely passive. An appearance of complex wing action is the result of reaction with the air of the various flexible wing elements. Forces on the elastic wing during the flap account for the changing angle of attack and shape of the wing, both sideward and rearward.
This natural spring pendulum effect conserves energy for the organism. Pivoted wings and pivoted fins such as described in much of the prior art referenced herein require energy to stop motion in one direction, then start up a reverse motion. This would be the case even in the frictionless vacuum of our example. This energy is lost on every stroke and significantly reduces efficiency. All of the referenced prior arts have this disadvantage.
Although most of the prior arts mention wing flexure, the described embodiments are substantially inelastic compared to the instant device. A large value for flexure as proposed herein is unanticipated in the prior art, as evidenced by the fact that the prior art suggests variability in the rate at which the wings are flapped. Conflict results when highly elastic wings are pumped at other than the natural frequency of the wings. They do not flap smoothly, but instead sustained pumping tends to create erratic, interfering vibration along the span with a reduction of distal end displacement. This effect is minimal and therefore obscured if the flexure is slight, as proposed by the prior art. The instant invention employs highly elastic wings operating at a singular natural frequency to increase efficiency.
A further distinction between the present invention and the prior art is that the prior art employs wings in hinged communication with the body of the device. The preferred embodiment of the present invention describes fixed attachment of the wings to the body. A hinged embodiment of the present invention is described as an alternative method to produce elasticity near the body of the device, but the device continues to operate as a springboard having high elasticity and therefore a singular natural frequency, which is unanticipated by the prior art. The utilization of elastic elements in the prior art is only suggested as an optional energy storing method as in the DeLaurier references. Elastic elements as suggested for use in the instant invention are also usable in conjunction with a firm connection of the wings to the body. This configuration is further distinguished from the prior art in that the hinges of the instant invention do not need to be adjustable sideward as in prior art DeLaurier wherein special hinges are designed to adjust translationally during pumping to effectively communicate a vertically moving panel with a pivoting panel. The referenced prior art of Bowers contains a similar problem.
Another novel element presented herein is illustrated as a bent configuration of the wing spar close to the point of fixed attachment to the fuselage. The wing spar is the principal resilient element providing elasticity to the wing. This crook configuration redirects the vertical forces produced during flapping into substantially horizontal forces. These horizontal forces are counteracted by the opposing forces produced by the other wing. This process substantially reduces the up and down movement of the fuselage which normally occurs in response to center of gravity changes caused by the flapping. It is proposed herein that birds have a similar bone structure which accomplishes the same task, the “wishbone” being the critical central element. None of the prior art suggests such a configuration and teach away from such a solution, since such a solution requires firm connection between the wings and body. Prior art DeLaurier shows a 3 part wing design that moderates such body oscillation. This aspect is therefore a further indication of the novelty of the instant device. Birds and other creatures fly utilizing the principles mentioned, whereby the actions of two wings provide impetus for forward motion and aerodynamic wing shape thereafter provides lift. The wings are fixedly attached to the body and act simultaneously at a singular flapping frequency. Although bird structure appears complicated, it is suggested herein that the “wishbone” is the fixed central element of the two wings, and thereby the point at which each wing is communicated. It is submitted that the “wishbone” provides much of the necessary resilience for flying, since it is typically observed to be flexible, it is of a shape which suggests flexibility, and it has a significantly larger cross sectional area than many other bones. It is also observable that there is minimal vertical oscillation of the body of birds during flight, a further indication of a springboard configuration such as proposed herein.
The natural frequency of the wings of particular flying organisms is dependent upon several factors. Span, surface area, wing shape and composition, flexure, and the density and viscosity of the air at any particular time are some of the determinants of an oscillatory flapping rate. It is submitted herein that increased velocity of birds in free flight is caused by an increased amplitude of the flap, not an increase in flapping frequency. Since a singular flapping rate is an important aspect of the instant device, methods for the determination of that rate are suggested. The prior art continually teaches a varying flapping rate in order to compare performance, and it is submitted herein that any pumping frequency other than the natural frequency reduces efficiency in a highly elastic device.
A natural spring pendulum works effectively only if the organism exerts a complementary force on the wings at a frequency matching the natural frequency of the wings. In much the same manner as pushing a person on a playswing or bouncing on a diving board, force must be applied in harmony with the natural frequency. If a repetitive force is applied at other than the natural frequency, conflict is created and energy is lost. Similarly, if muscular forces are applied at intervals other than the natural frequency in natural fliers, energy is lost. It may again be noted that the frequency is substantially independent of the distortion of the wing. During sustained flight, larger strokes maintain the natural frequency. This principle is fundamental to all types of pendulums, and was first observed by Galileo.
The concepts associated with natural spring pendulums are herein applied to flying devices. The pumping force may be applied by a variety of methods, including motorized and human means. Since application of the pumping force necessarily must be in synchrony with the natural frequency of the wings, a method by which a pumping means is activated at the correct time and in the correct direction is addressed. None of the prior art addresses this issue. A man-powered device would utilize the “feel” of the pendulum for applying the force. However, a completely mechanical device must successfully match the natural frequency. One method by which this may be accomplished is by sampling the wing motion, and thereafter switching the pump on and off with appropriate directional changes at the maximum displacements. This feedback process automatically adjusts for variations or interruptions in the flapping. Optionally, the wing frequency could be mathematically derived or experimentally determined and thereafter a pumping means with the desired frequency could be utilized during operation. The instant preferred embodiment illustrates a means to apply force to the wings which is similar to an escapement mechanism used in mechanical clocks. By this method, power is sympathetically applied to the wings at the correct time and in the correct direction, thereby facilitating the process and also saving energy. A further embodiment teaches a sampling and pumping means which is electrical. Such means to harmonically pump wings is not anticipated by any prior art. A problem of “backloading” as described in prior art by DeLaurier is eliminated if the pumping of the wings is in synchronous agreement with the natural movement of those wings.
Wing composition and design presented herein allows for flexible flapping and aerodynamic shape. The preferred embodiment describes a double aerofoil wing design having a flexible supporting spar with chords extending substantially perpendicularly. The structure is covered with a lightweight pliable plastic material. A molded wing embodiment is also suggested.
Wing structure of the instant device provides for flex not only in a spanward direction, but also rearward with respect to the direction of motion. The leveraged force on the trailing wing edges causes the wing structure to undergo pitching during each flap. This aspect will be discussed in the specification. Such flapping provides a substantially continuous rearward-directed reaction with air, thereby propelling the creature forward. Aerodynamic wing design causes lift when such forward propulsion is provided, allowing the bird to stay aloft. Additionally, a wing structure such as existent in birds approximates a class III lever wherein the proximal fixed end acts as a fulcrum, a pumping force is applied near the fulcrum, and thereafter a large distal-end distortion is created. A large distal displacement is especially advantageous for flying, since air has such a low viscosity. None of the prior arts showing high elasticity teach a pumping structure which applies a force between an end attached to the fuselage and an end that is free to elastically flap. This is a further distinction of the instant device from the prior art.
Wing shape is another distinguishing factor in flapping performance. By angling the nearer portion of the wing forward and the outer portion of the wing in a rearward direction, the flapping of the wing tips is directed more toward the rear, providing a greater displacement of air in that direction. In this manner, the common “V” shape of many bird wings directs the air more rearwardly, thereby increasing forward thrust.
Since the instant device presents a substantially passive, highly elastic wing which is driven by a force applied near an end proximal to the body, the weight of the wing itself causes a downward curvature. The wing therefore must be initially angled upward from the body to counteract this downward curvature to insure that the entire wing structure reacts with air substantially in a horizontal manner. This curvature is observed in many birds and is proposed in the instant device.
Wing flexure in the rearward direction is also important. This flexure is common in nature and is substantially produced by resilient feathers. Rearward wing edges are more pliable than leading edges since rearward wing tips are comprised of singular feathers having their most flexible parts exposed and substantially rearwardly directed. A flexibility gradient exists from front to rear whereby the wingtip feathers are oriented such that stems and barbules of the individual feathers are most pliant in a substantially rearward direction. Distal wing tip feathers of birds, for example, have stems which are directed more or less spanwardly, and have flexible surfaces which are created by a multiplicity of barbules extending from these stems. These wing tip feathers are asymmetric, with a wider, more elastic barbule surface directed rearwardly. The embodiments of the instant device describe such a flexibility gradient. Flexure of the rearmost elastic elements of the wing creates a secondary vertical elastic flapping effect which is slightly out of phase with the primary, spanward, frequency of the wing and reacts with vortices created by previous strokes thereby forcing air to the rear of the device and increasing leading edge suction.
The instant invention also addresses the importance of wing camber. In nature, bird wings are cambered to provide lift when propelled forwardly, a feature which has been successfully imitated by man in the design and construction of airplane wings. It is submitted herein that this camber produces an important secondary effect. Since the curvature is concave downward, as in a Roman arch, the wing is more resistant to flexure when moving downward and, conversely, flexes more readily when moving upward. Flapping, therefore, produces a reactive and powerful downstroke. Since the upstroke is thereafter more flexible, it does not generate the power that the previous downstroke produced and allows air to pass through with less resistance. Such unequal vertical flexure is therefore helpful in keeping the device aloft. The prior art of DeLaurier argues that downstrokes require significantly more power than upstrokes, and suggests that birds solve the problem by wing contraction or rest periods during upward strokes of the wing. It is suggested herein that the differential vertical flexure of highly flexible cambered wings, such as proposed in the instant device, substantially addresses this problem. Additionally, wing tips of birds have singular feathers which are individually cambered. Both the stems and the barbules of these feathers have a downward curvature. In a manner similar to the spanward wing surface, this cambering of wingtip feathers decreases resistance during the half-cycle upstroke of the wingtips and presents increased resistance during downstrokes, thereby creating a more powerful downstroke than upstroke. A further differential between downstrokes and upstrokes is caused by feather overlap and is addressed in the instant device. No prior art proposes such means to provide unequal powered strokes.
The prior art in this field does not show other novel aspects presented by the instant invention. Most of the prior art proposes hinged wings, a disadvantage already discussed. Prior art U.S. Pat. No. 5,899,408 shows a flying device designed to utilize a singular flexible wing. While this reference mentions harmonic oscillation in its operation, it varies significantly from the instant device in many ways. The reference does not firmly attach wings to the body of the device, but instead attaches a single wing, spanning both sides, to a powered armature pumping at a central location of the singular wing. The wing is therefore moveable with respect to the body of the device and therefore requires slots on the sides of the fuselage through which the wing may slide vertically during oscillation. The single wing concept of the reference does not anticipate the instant device because the instant device presents springboard wing structures which are immoveable at an end with respect to the body of the device while being driven up and down at a point outward of the body. Connection to the fuselage of the Bowers design would be difficult at best; possibly pivoted communication at the two nodal points along the wings thereby resulting in a design similar to the DeLaurier references. Additionally, U.S. Pat. No. 5,899,408 mentions oscillatory action, but thereafter does not describe means for accomplishing that action nor specify the existence of a singular natural frequency. Recognizing and producing such a unique natural frequency is not obvious. An important difference in the design of U.S. Pat. No. 5,899,408 from that of the instant device is that lift is provided by a valve structure on the wing surfaces which allows air to flow through the wings on upstrokes and thereafter precludes the same from occurring during downstrokes. The present device provides lift by the natural combination of flexible wing and wing tip cambering, overlap, and aerodynamic cross-sectional shape along with a forward impetus provided by large spanward distal displacement and flexible rearward reaction with air. Additionally, this reference does not teach a highly elastic wing construction, and teaches toward less elasticity by describing a desired unequal lift caused by a valved wing structure with substantially no rearward wing flexure. As mentioned previously, many features presented herein affect successful flapping propulsion, none of which are significantly addressed or suggested by U.S. Pat. No. 5,899,408 and therefore that prior art does not anticipate the many advantages of the instant device.
The prior art of Velkow recognizes the necessity for wing elasticity in both span (sideward) and chord (rearward) directions, but proposes various flapping rates and uses mechanical means to flex only the outer part of the wings. The wings are pivotable at the proximal end, and flexure is achieved at the distal end by means of an elasticized pulley mechanism which retracts and extends with the pumping of the drive mechanism. It is submitted herein that flexure of the wing is best acquired along the entire length, with springboard connection to the fuselage at the proximal end. Energy storage is important, and employing the entire wing for such storage is an aspect which is not obvious. Velkow also does not address the necessity for a singular pumping frequency associated with any particular wing which must be energized at that frequency, and therefore that prior art does not describe a means to acquire such a frequency. A further aspect which is not addressed in the Velkow references is the cambered flexibility of the wings and wing tips to attain differential half-cycle power. Lastly, Velkow does not teach a forward then rearward lateral wing design which is extant in the present device for improving rearward air displacement at the distal end of the wing.
The construction of the instant device is unobvious since one skilled in the art would be reluctant to build a device having highly flexible wings and which are not pivotable. It is likely that immoveable connection of a wing to the body has been overlooked since a primary consideration of a flapping device is to make the flapping less difficult, and firm connection initially seems to conflict with this concept. It is both unlikely and unobvious that consideration has been given to the advantages produced by a firm springboard connection of elastic wings to the fuselage. Therefore, most of the referenced prior art describes hinged connection, and because some success has been attained, a springboard configuration was not envisioned as being able to produce better results. It follows that consideration of frequency matching with respect to the natural frequency of the wing is not an obvious concept and the successes of fixed wing aircraft also tend to obscure the characteristics of effective elastic flapping flight.
The features of the instant device are submitted by the applicants to be novel and unobvious in light of the prior art. Additionally, the combination of the various elements of the device presented herein is also submitted as being unobvious and novel to those skilled in the art. Details of those various elements are given in the description of the preferred embodiment of this specification.